Vitodens 100 - Powerful enough

[rtukuk]

Hi, I have moved into a large 4 bed 3 bathroom house recently and it had a Vitodens 100 boiler fitted new about 15 months ago (with no documents). An engineer has replaced the pump with a Grundvos and I have had it serviced and checked by 3 engineers. There are 14 radiators (6 down, 8 up) but none ever get very hot, lukewarm at most. Most of the rads are small / double but there is one 2m double radiator that never gets very warm in particular.
All have been balanced and bled. For example, this morning despite the heating being on 2 hours solid, I can't get it warmer than 19c. I have new top spec windows, 300mm of loft insulation and foil behind the rads.

My question is:
Do you think the Vitodens 100 is powerful enough for 14 rads or did the previous owners put in a lower spec boiler cheap so they could still sell when the pervious boiler went wrong?
I have been told to look at the data badge on the boiler which will tell me what the output is(on the top to the right of the flue outlet) but I'm not sure if I have to take it to pieces to do this.

Thanks
[email protected]

 

[ChrisR]

It's a 24-30kW boiler so yes it's (assuming normal/sensible radiator sizes) big enough to heat the house, without straining. See http://www.viessmann.co.uk/en/products/gas_fired_condensing/vitodens_100-w_.html


This boiler usually has some form of Weather Compensation implemented, which is what's controlling it. If the house isn't hot enough, it's probably set up wrongly, which is tiresomely common, though that could be masking a problem in the boiler.

Unless you have sludge, the extra-cool rad is a sign of improper balancing in the system.

You need a heating engineer with more knowledge that about 95% of the ones out there to see what's been done to the boiler, and sort out the balancing.

If you're the sort of chap who doesn't have problems programming the proverbial video, then you're probably best to read all you can about how the boiler's supposed to work and alter the controls yourself.

 

[rtukuk]

Hi,

Thanks for the response.
Are they all 30kw or does it vary? Vitodens (who weren't particulaly helpful) suggested I check to see what the output was on the flue outlet. If it's only 26w would that be sufficient for 14 rads over a large area.

I'll get the Weather Compensation checked out.

I did notice when the hot water was on in summer and the heating off, the rads did get slightlly warm so I'll let the splitter (sorry don't know name) replaced but I don't know if this is affecting the heat in the rads.

The boiler does seem to heat up the water and shows up to 64c but this just doesn't seem to reflect in the radiators for some reason. The house is about 20 years old.

 

[JohnD]

is it the combi or the regular boiler? If it has a cylinder, is the cylinder unexpectedly hot?

is it a pressurised system or does it have a feed and expansion tank in the loft?

if you turn the boiler stat up, what is the highest temp it will display, and how many burner bars show?

when you feel your radiators, are any of them too hot to hold, top and bottom? When you bleed them does any gas come out?

Is there any sign of a by-pass?

is the rest of the system (except the boiler) old?

have you got thermostatic radiator valves?

when you feel the flow and return pipes coming out of the top of the boiler, is the flow (right hand pipe) too hot to hold, and the return (left hand pipe) too hot to hold for long?

give us an example of the size of a room, and its windows, and the size of the radiator in that room?

is there any unusual heat loss, such as thin loft insulation, large windows, or internal doors left open?

what is the setting on the room stat?

BTW I have a Vitodens 100 Compact, with 9 radiators and a cylinder, and this frosty morning it took about half an hour to come to 70°C, at 4 burner bars displayed

 

[Agile]

You seem happy to post here but reluctant to look at the data label on the top of the boiler.

So far we dont know if its a combi or heat only boiler. Where do the pipes come out? Do you have a cylinder?

Is it a microbore system with pipes only 10mm or smaller to the rads?

You say 3 engineers have "looked" at the boiler. I would suggest all you need is one competent one. As Chris says 95% of the people you might call might not be able to know how to specify and set up your system.

Whilst until you have looked at the data plate I wld not guess at the power but the power is likely to be perfectly adequate.

If you have not looked at the data plate,have you even looked at the temperature knob on the front of the boiler? When is it set?

Tony

 

[rtukuk]

All
Thanks for the responses.
Apologies, I've just looked on top of the boiler and seen the label. I assumed I would have to take the case off..

I've added 2 photos to show the sticker on top and also the boiler when on the max setting after about 15 mins (at 73c). Normally it only goes up to 65c approx.
//www.diynot.com/network/rtukuk/albums/

I've just checked it and it was on 46c and then the burner activated and it went to to 65c in about 20 seconds and turned the burner off again.

I always have it set on the middle setting with a dot which I assume is the optimum for economy?

I do have a cylinder and this gets hot. I'm not sure whether it's excessively hot or not.
I'm not sure if it's a combi or regular - I thought it was a condensing boiler (is that different)?

I'm not sure if it is Microbore but the house is 22 years old.

I agree about your comments on getting a competent engineer. The last time I went to the Vitodens web site and used one of their approved engineers who seemed a bit better but quite young.

There is a tank in the loft also but I thought this was for cold water (?)

I don't know if it's pressurised, is there an easy way to tell?

The highest temp it showed was 73c and it had 2 bars on. Sometimes I have seen 4 bars on though when it's operating normally.

I have bled all of the radiators quite a few times and air only came out the first time. I would describe them all as lukewarm or just slightly better. At my last house, some were too hot to touch. The largest room has a large double radiator and this get's the least warm and is colder at the bottom despite bleeding it. This is a replacement new rad but is balanced to be fully open. It's almost like it's too big for the circuit.

I don't know if there is a bypass or how to check for this.

The rest of the system apart form the pump and the boiler are original 22 years old apart form the one large radiator in one bedroom which looks newer and I think is a replacement.

I have thermostatic valves upstairs and turn off what we don't use.

On the flow and return pipes coming out of the top of the boiler, the flow is too hot to hold, and the return pipe is hot but not as hot as the flow pipe.

See a link for the house and room sizes:
http://www.vebra.com/property/2311/13207888

There are some large windows but all are now new. The loft is very well insulated with 300mm and we generally shut internal doors.

The room stat is programmable and normally set at 18c at night, 22c in the early morning and evening and 21c in the day.

Sorry I can't answer any more questions better, as you can tell I'm an absolute novice as far as boilers go but keen to understand them better.

 

[JohnD]

the return pipe on the boiler, is it hotter than the radiators?

presumably the cylinder has a thermostat on it. When the cylinder comes up to temp, this should click and the hot flow from the boiler to the cylinder should stop. After 10 mins or so you should observe the pipes starting to cool. This will usually be done by a 3-port valve (T-shaped with a squarish metal motor box at the apex) closing off the pipe that goes to the cylinder. See is this is working. You can adjust the cyl stat down a bit using a medium screwdriver and you may hear it click. The normal setting should be about 60° C and has to be lower than the boiler, or the boiler will never stop trying to heat it

What I am thinking of here, is that if the boiler is coming up to the set temp (usually between 60 and 70 but you can adjust it up to a max of about 80), and the heated water is being pumped round, then if it is not going through the rads, the flow may be going through something else, typically a bypass valve (which links the flow and return pipes when all the rads are closed) or through the cylinder coil, if it is not shutting off, or perhaps it is pumping over in the loft into the feeds and expansion tank. Go and have a look.

If you system does not have an F&E then it will be pressurised and there will be a pressure gauge on the boiler.

 

[Agile]

Its a 24 kW heat only boiler.

Can you feel the pipes in/out of each rad?

Also surely you can measure the diameter of the pipe?

It could be that the supply to the cylinder is not turning off when its heated up and is not balanced properly.

However it looks as if you need a competent engineer and the one from the Viessmann site should be OK

Tony

 

[rtukuk]

The return pipe on the boiler is hotter than most if not all the radiators.

The cylinder has a stat and this is set to 60c
I've added some new pictures showing this.
I've measured one of the pipes going into a radiator and it is 19mm diameter.

I wonder with the fact that the switch box is original and also that the rads heat slightly when on hot water only in summer, whether you are right and this could be at fault. Could it be some of the hot water for the heating system is bypassing the rad system?

I've felt the in and out pipes on the rads and wouldn't say any are really hot. About the same temp as the rads

Sorry, what is an F&E?

 

[JohnD]

The return pipe on the boiler is hotter than most if not all the radiators.

The cylinder has a stat and this is set to 60c...

Sorry, what is an F&E?

If most of the water is going through the rads, then the boiler return pipe will be no hotter than the rad return pipes. So some of the flow is going somewhere else.

Turn down the cyl stat. 50C will be enough for a day or so while you work out what is happening. If you use a medium screwdriver in the plastic spindle you will hear it click when it goes off. It is important to do that. If you have a thermometer you can test the tap water tomorrow and see if it is significantly hotter than the cyl stat setting (they are not very accurate). You should find that the pipes going into the side of the cyl cool down after you have clicked the cyl stat off. Have you found the 3-port valve yet? It is probably close to the cylinder and/or the pump and/or the boiler.

Turn off those rads that are hottest, and especially towel rails which are sometimes plumbed differently.. If the system is badly balanced, it is common for a few radiators to take all the flow, leaving nothing for the cooler ones. If the cooler rads then get hot, we can explain how to balance the system so that all get equally hot.

Feed & Expansion Tank. Usually in the loft. About 2ft long x 1ft wide x 1ft high, with a ball valve in it like in a toilet cistern. Your Vitodens looks to me like an open-vented one as I see no pressure gauge, therefore I expect it to have an F&E. Have a look and see what colour the water is; is it warm; is there mud in the bottom. There is a strong chance that your heating system has sediment in it, but we will think about that later.

Turn up the temperature knob on the boiler. Mine goes to 80C when wound as far clockwise as it will go.

Have you got thermostatic radiator valves? Turn them to their highest setting (except for the rads you are going to turn off)

A typical 3-port motorised valve. It has a electric cable to operate it.

 

[Agile]

Setting the boiler flow to 72° C will enable it to continue to operate efficiently and if you do what john has described it will turn off the cylinder as soon as the water reaches 50° C and then Iexpect the rads will heat up properly.

Tony

 

[rtukuk]

Hi, I noticed a whining and grumbling sound coming from the boiler this morning and it now has a SERV light on. It constanly keeps firing for a few seconds and then taking the temperature up to about 85c then stopping the burner for a few seconds then re-starting it all over again. I'll get the Vitodens approved plumber I used before to look at this and also check the 3 point valve asap. I'll let you know the outcome out of interest.

Do you think it's safe to keep on? It keeps constantly making a noise.

 

[rtukuk]

All - to add to my last mail, I've now turned it off / on and it seems back to normal. The temperature is back down, the noises have stopped and the fault has disappeared. I'll still get an engineer to come and look though.

 

[mysteryman]

When the word 'SERV' appears, the boiler is in emissions test mode, something that is done annually in Germany, so the burner runs flat out. It is done by turning the boiler thermostat briefly to maximum and back down.

These Vitodens 100 Compact Heat only boilers have a return temperature sensor, and are designed to work at a Delta T across the boiler of 20C. If the return temperature rises above 50C, it begins to modulate, regardless of the flow temp. If you reduce the pump speed, the Delta T increases, and you get a higher flow temperature with the same return temperature. None of this applies to the Combi or System versions, which do not have a return temp sensor.

On an S or Y Plan, you need the flow temp as high as possible - the dot setting will endeavour to keep the boiler condensing, but you won't get the cylinder hot enough.

Please note that the Vitodens 100 type WB1A Compact is the ONLY Vitodens that CANNOT have weather compensation applied via on-board controls. You can do it with all others including the later type WB1B Compacts.

 

[JohnD]

When the word 'SERV' appears, the boiler is in emissions test mode, something that is done annually in Germany, so the burner runs flat out. It is done by turning the boiler thermostat briefly to maximum and back down.

That's a handy trick! I just did it on mine, flow went from 56° to 82° in about a minute.

I suppose it was a fast but uneconomical way of getting my rads extra-hot on a chilly morning.